This invention relates generally to a method and apparatus for producing continuous tone images with near photographic print qualities using xerography.
In the practice of conventional xerography, it is the general procedure to form electrostatic latent images on a xerographic surface by first uniformly charging a charge retentive surface such as a photoreceptor. The charged area is selectively dissipated in accordance with a pattern of activating radiation corresponding to original images. The selective dissipation of the charge leaves a latent charge pattern on the imaging surface corresponding to the areas not exposed by radiation.
This charge pattern is made visible by developing it with toner by passing the photoreceptor past one or more developer housings. In monochromatic imaging, the toner is generally comprises black thermoplastic powder particles which adhere to the charge pattern by electrostatic attraction. The developed image is then fixed to the imaging surface or is transferred to a receiving substrate such as plain paper to which it is fixed by suitable fusing techniques.
Recently, there has been a great deal of effort directed to the development of color copiers/printers which utilize the xerographic process. Such efforts have resulted in the recent introduction of the Xerox.TM. 5775.TM. copier/printer and the Fuji XeroxA-Color 635 machine.
The quality of color xerographic images on paper has approached the quality of color photographic prints. However, color xerographic prints fall short because they do not have the uniform gloss, dynamic range or brilliance typical of photographic prints. Nor do xerographic prints have the feel of photographic prints because the paper usually used is too lightweight and too limp.
Typically the surface of color toner images is irregular, therefore, rather rough or lumpy. The behavior of incident white light vis-a-vis such color images is believed to be as follows:
Some of the white light incident on the substrate carrying the color toner images specularly reflects off the substrate. PA1 Some of the light goes down into the paper, scatters around and comes back out in various directions, some through the toner and some not. PA1 Because the toner surface is rough or irregular some of the light incident thereon is reflected off the toner in various directions. PA1 Some of the light incident on the irregular toner surfaces passes through the toner into the paper and comes back out in various directions. PA1 contacting an image (preferably multi-toned image) with a transfer web (intermediate receptor layer) comprising in sequence, a carrier layer, a transferable release layer, and a releasable adhesive layer (releasable from the carrier layer along with the transferable release layer so that both layers transfer at once), said adhesive layer being in contact with said toned image, said contacting being done under sufficient heat and/or pressure to enable said toned image to be adhered to said releasable adhesive layer with greater strength than the adherence of said toned image to said imaging surface of said photoconductive layer; PA1 separating the transfer web and said photoconductive layer so that the toned image is removed from said photoconductive layer and remains adhered to the adhesive layer of the transfer web; PA1 contacting the surface of the transfer web having both the multi-toned image and adhesive thereon with a permanent receptor surface; PA1 adhering the adhesive on the transfer web to the permanent surface; and PA1 removing the carrier layer of the transfer web from the adhesive and the release layer of the transfer web so that an image article is formed of the permanent receptor, multi-toned image, releasable adhesive, and the resultant surface coating of the release layer which is furthest away from the permanent receptor.
White light becomes colored due to selective absorption as it passes through toner. The light then goes down into the paper and back out through the toner whereby it becomes more colored through more absorption. As will be appreciated, any white light which does not pass through the toner diminishes the appearance of the final print.
Attempts to make up this deficiency in conventionally formed color toner images have led to the lamination of xerographic images on paper using a transparent substrate. This procedure has been only partially successful because the lamination process tends to reduce the density range of the print resulting in a print that has less shadow detail. The lamination process also adds significant weight and thickness to the print.
Additionally, it is believed that the aforementioned lamination process does not produce good results because typically the color toner images at the interface between the laminate and the toner do not make suitable optical contact. That is to say, the initially irregular toner image at the interface, is still irregular (i.e. contains voids) enough after lamination that light is reflected from at least some of those surfaces and is precluded from passing through the toner. In other words, when there are voids between the transparency and toner image, light gets scattered and reflected back without passing through the colored toner. Loss of image contrast results when any white light is scattered, either from the bottom surface of the transparent substrate or from the irregular toner surfaces and doesn't pass through the toner.
A known method of improving the gloss of color xerographic images on a transparent substrate comprises refusing the color images. Such a process was observed at a NOMDA trade show in 1985 at a Panasonic exhibit. The process exhibited was carried out using an off-line transparency fuser, available from Panasonic as model FA-F100, in connection with a color printer which was utilized for creating multi-color toner images on a transparent substrate for the purpose of producing colored slides. Since the finished image from the color printer was not really suitable for projection, it was refused using the aforementioned off-line refuser. To implement the process, the transparency is placed in a holder intermediate a clear relatively thin sheet of plastic and a more sturdy support. The holder is used for transporting the imaged transparency through the off-line refuser. After passing out of the refuser, the transparency is removed from the holder. This process resulted in an attractive high gloss image useful in image projectors. The refuser was also used during the exhibit for refusing color images on paper. However, the gloss is image-dependent. Thus, the gloss is high in areas of high toner density because the toner refuses in contact with the clear plastic sheet and becomes very smooth. In areas where there is little or no toner the gloss is only that of the substrate.
The following is a discussion of prior art which may be relevant to the patentability of the present invention:
U.S. Pat. Nos. 4,686,163 and 4,600,669 describe an electrophotographic imaging method that uses an element comprising a photoconductive layer on an electrically conducting substrate capable of transmitting actinic radiation to which the photoconductive layer is responsive, and a dielectric support, releasably adhered to the substrate, comprising the photoconductive layer or an overcoat thereof forming a surface of the element capable of holding an applied electrostatic charge. To use the element, the surface of the dielectric support is charged, and the photoconductive layer is imagewise-exposed to actinic radiation, thereby forming a developable electrostatic image on the dielectric surface. The electrostatic image, in turn, is developed with toner to form a first color image. A composite color image is formed on the element by repeating the sequence one or more times with imagewise exposure of the photoconductive layer to actinic radiation transmitted through the substrate, and developing over each preceding image with a different color toner. The composite toner image is transferred with the dielectric support to a receiving element to form a color copy such as a three-color filter array or a color proof closely simulating the color print expected from a full press run.
The dielectric support on the photoconductive layer comprised a transparent blend of poly(vinylacetate-co-crotonic acid, 95/5 mole ratio) and cellulose acetate butyrate. The resulting multicolor proof presented a multicolor toner image against a white paper background and protected by the overlying dielectric support, thus accurately resembling a multicolor print from a full press run.
The receiver element to which the dielectric support and composite toner image are transferred can be any suitable material against or through which the toner image is desired to be viewed. The receiver can be print stock, such as paper, upon which a press run will be conducted. The receiver can also be of transparent material such as a polymeric film. With respect to the latter, the invention also contemplates, as an embodiment, transfer of the composite toner image and dielectric support to image-bearing elements such as microfilm or microfiche so that the composite color image forms information in addition to image information already present on such image-bearing elements. In addition, the invention contemplates the use of transparent glass or nonbirefringent translucent polymeric materials such as cellulose esters for use as the receiver. Receivers manufactured from such materials are suited for use in forming three-color filter arrays by the process described herein involving the formation of filter array matrices of the complementary colorants cyan, magenta and yellow in the respective color toner imaging steps. If desirable, the receiver can also contain a suitable overcoat layer adapted to soften under the influence of pressure and heat during the transfer step. In this manner, the adhesion of the dielectric support and composite toner image to the receiver can be enhanced.
The electrophotographic element bearing the multicolor toner image is moved to a separate lamination device comprising heated metal and rubber rolls, together forming a nip. The toner image is passed through the nip with and against a white receiver paper at a roll temperature of 100.degree. C. (212.degree. F.) and a pressure of 225 pounds per square inch (1.551 MPa) to effect transfer of the dielectric support and composite image to the receiver followed by peeling off the rest of the electrophotographic element.
U.S. Pat. No. 4,066,802 granted on Jan. 3, 1978 to Carl F. Clemens discloses a method of decalcomania in which a toner image pattern is formed on a transfer member which has been overcoated with an adhesive material. A polymeric sheet is interposed between the toner image and a cloth or other image receiving medium. The polymeric sheet assists in the permanent adherence of the toner imaging pattern to the cloth material or other medium when the composite is subjected to heat and pressure. The transfer member and method of its use are set forth. Another embodiment discloses the use of solvent to fix the image to a cloth material.
U.S. Pat. No. 5,065,183 granted on Nov. 12, 1991 to Morofuji et al discloses a multicolor printing method for printing multicolor picture images upon a material or object to be printed comprises the steps of, in accordance with a first embodiment of the invention, the formation of a multicolor toner image upon a flexible belt by means of electrophotographic printing methods or techniques, and the transfer of such multicolor toner image directly to the material or object to be printed, such as, for example, a container made of, for example, metal, paper, plastic, glass, or the like, by means of a thermo-transferring process. In accordance with a second embodiment of the invention, the multicolor toner image is formed upon a plastic film, which is laminated upon the flexible belt, by means of electrophotographic printing methods or techniques, and the plastic film is then transferred to and fused upon the container. In accordance with a third embodiment of the invention, a photoconductive member is irradiated by means of exposure light upon a rear surface thereof wherein the multicolor picture images are also formed by electrophotographic printing methods or techniques. In this manner, previously formed toner images upon the photoconductive member do not interfere with the image exposure processing.
U.S. Pat. No. 5,126,797 granted on Jun. 30, 1992 to Forest et al discloses a method and apparatus for laminating toner images wherein a toner image on a receiving sheet is laminated using a transparent laminating sheet fed from the normal copy sheet supply of a copier, printer or the like. The laminating sheet is fed into laminating contact with the toner image after the toner image has been formed on a receiving sheet. The resulting sandwich is fed through the fuser laminating the image between the sheets. The invention is particularly usable in forming color transparencies.
U.S. Pat. No. 5,108,865 granted to Zwaldo et al on Apr. 28, 1992 discloses a method including the steps of:
U.S. Pat. No. 4,949,103 granted to Schmidlin et al on Aug. 14, 1990 discloses a direct electrostatic printing (DEP) device utilized for printing mirror or reverse/wrong reading toner images on a transparent substrate. An adhesive coating on the transparent substrate on the toner image side thereof enables the transparent substrate to be affixed to a substrate such as an envelope such that the mirror images are right reading.
U.S. Pat. Nos. 4,868,049 and 4,724,026 granted to Marshall A. Nelson on Feb. 9, 1988 and Sep. 19, 1989, respectively disclose selective metallic transfer foils for selectively transferring metallic foil to xerographic images on a receiving substrate such as paper. The transfer sheet comprises, in successive layers, a carrier film, a metallic film and an adhesive, the adhesive containing a dispersion of 0.5 micron or larger particulate material. A method is disclosed for forming images overlaid with metallic foil. According to the method of the invention, a sheet comprising xerographic images is provided and placed in face-to-face contact with a metal transfer sheet, to form a sandwich with the xerographic images on the inside. Heat and pressure are applied to the sandwich, causing the xerographic images to become tacky and causing the metallic foil to selectively adhere to the images. The remainder of the transfer sheet is then stripped away from the resulting decorated sheet comprising xerographic images overlaid with metallic foil.
In the preferred embodiment of the invention, the metal transfer sheet is provided with an adhesive of high filler content resin which has been found to produce good quality transfers to xerographic images produced by a wide variety of toners and photocopy machinery.
U.S. Pat. No. 3,914,097 granted to Donald R. Wurl on Oct. 21, 1975 discloses a sheet guide and cooling apparatus for preventing curl in sheets bearing a developed image, the image being permanently fixed to the sheet by application of heat and pressure. The apparatus is positioned to have a flat thermally conductive surface establishing a path for the sheet, downstream of the fixing area, the path extending in a plane substantially coplanar with the plane of sheet travel in the fixing station. Vacuum means associated with the surface maintains successive incremental portions of a sheet in face-to-face contact with the flat surface as it is being guided for at least a predetermined period as the sheet moves along the path and furthermore, provides a flow of cooling air for the surface.
U.S. patent application Ser. No. 08/095,639 filed on the same date as the instant application discloses a method and apparatus for creating simulated photographic prints wherein a mirror image is formed on a transparent substrate. The transparent substrate has bonded thereto a backing sheet which serves as protection for the powder images on the transparent substrate as well as a reflective backing which significantly enhances the look of the images. The transparent substrate and backing sheet are bonded together by simultaneously passing the two members between a pair of heated rollers while simultaneously applying pressure.
U.S. patent application Ser. No. 08/095,622 filed on the same date as the instant application discloses a device for creating simulated photographic prints. A transparent substrate to which a reverse reading image has been fused is uniformly coated on the image side thereof with a white material which serves a the reflective backing.
U.S. patent application Ser. No. 08/095,016 filed on the same date as the instant application discloses a device for creating simulated photographic prints. As disclosed therein, a transparent substrate with a reverse reading toner image thereon is bonded to a backing sheet using heat and pressure provided by a pair of heat and pressure roller members. A second pair of rollers is provided downstream of the the heat and pressure roll pair receives the lead edge of a simulated photographic print and serves to pull the print in order to flatten it. A vacuum holddown transport downstream of the puller rolls serves to further flatten the print during a cool-down period.
U.S. patent application Ser. Nos. 08/095,790 and 08/095,136 filed on the same date as the instant application discloses a device for creating simulated photographic prints wherein a transparent carrier having a xerographically formed mirror image fused thereto is bonded to a plastic substrate through the use of heat and pressure. The transparent carrier and the plastic substrate form the finished print.